Signals may be modulated according to a differential phase-shifted keying (DPSK) modulation technique. According to the technique, changes in the phase of a signal are used to represent bit data. A modulator at a transmitter translates a bit sequence into phase changes that represent the bit sequence. A demodulator at a receiver translates the phase changes to retrieve the bit sequence.
The demodulator may be monitored to determine whether the demodulator is properly demodulating the signal. Known techniques for monitoring a demodulator, however, are not satisfactory in certain situations. It is generally desirable to have satisfactory demodulator monitoring.